BR112019025937A2 - steel sheet for cans and production method for the same - Google Patents

Abstract

The present invention relates to a steel sheet for cans that exhibits excellent weldability; and a production method for it. This steel sheet for cans provided on the surface of a steel sheet in the order of the side of the steel sheet, a layer of metallic chromium and a layer of hydrated chromium oxide. The deposited amount of the metallic chromium layer is 65-200 mg / m2. The deposited amount of the hydrated chromium oxide layer in terms of chromium is 3-30 mg / m2. The metallic chromium layer includes: a base part with a thickness of 7.0 nm or greater; and granular protrusions that are provided in the base part that have a maximum grain size of 100 nm or less, and have a numerical density per unit area of at least 200 per µm2.

Description

“STEEL SHEET FOR CANS AND PRODUCTION METHOD FOR THE SAME”. TECHNICAL FIELD

[001] The present invention relates to a plate prepared for tinning and a method of manufacturing it.

PREVIOUS TECHNIQUE

[002] The cans, which serve as containers for drinks and food, are useful for storing the contents for a long period of time and, therefore, are used worldwide. The cans are roughly classified into the following two types: a two-piece can that is obtained by submitting a sheet of metal to draw, iron, stretch and fold to form a full can bottom and a can body and then join the body of the can with a top cover by sewing; and a three-piece can that is obtained by machining a metal sheet into a tubular shape, welding the tubular metal sheet by a wire stitching process to form a tin body and then joining the opposite ends of the can body separately with lids by sewing.

[003] Conventionally, a galvanized steel sheet (so-called tinplate) has been widely used as a sheet prepared for tinning.

[004] Currently, a steel plate treated with electrolytic chromate (hereinafter also called tinless steel (TFS)) with a layer of metallic chromium and a layer of hydrated chromium oxide, is expanding its range of applications, because it costs much less and is more excellent in adhesion to paint than tinplate.

[005] In connection with the reduction of residual washing liquid and CO for environmental reasons, cans using a steel sheet laminated with an organic resin film, such as PET (polyethylene terephthalate), call attention as a technique alternative that allows a coating process and a subsequent cooking process to be omitted. Also in this context, it is expected that the use of TFS with excellent adhesion to an organic resin film will expand continuously.

[006] However, TFS is sometimes inferior in weldability to tinplate. This is because, due to the cooking hardening treatment after painting or heat treatment after laminating an organic resin film, a layer of hydrated chromium oxide in the surface layer initiates a condensation reaction by dehydration, and this leads to increased contact resistance. In particular, the cooking hardening treatment after painting requires a higher temperature than the heat treatment after laminating an organic resin film and therefore tends to result in less weldability.

[007] Thus, for TFS today, a layer of hydrated chromium oxide is mechanically polished and removed immediately before welding, to make welding possible.

[008] In industrial production, however, there are many problems in which, for example, the metal dust generated by polishing can be mixed into the contents, a maintenance charge such as cleaning can-making equipment increases, and the risk of fire caused by metal dust increases.

[009] To deal with this, a technique for welding TFS without polishing is proposed, for example, by Patent Literature 1.

LIST OF QUOTES

PATENT LITERATURE Patent Literature 1: JP 03-177599 À

SUMMARY OF THE INVENTION TECHNICAL PROBLEMS

[010] In the technique described by Patent Literature 1, the treatment of anodic electrolysis is carried out between the cathodic electrolysis treatments of the anterior and posterior phases to thus form a large number of defect portions in a layer of metallic chromium, and then, the metallic chromium is formed in a form of granular protrusions through the treatment of posterior phase cathodic electrolysis.

[011] According to this technique, it is expected that, when welding, the granular protrusions of metallic chromium destroy a layer of hydrated chromium oxide, which is a factor that makes it difficult to weld on the surface layer, reducing the contact resistance and improving weldability.

[012] However, the present inventors studied the sheet prepared for tinning described specifically in Patent Literature 1 and found that, in some cases, weldability was insufficient.

[013] An objective of the present invention is, therefore, to provide a plate prepared for tinning with excellent weldability and a method of manufacturing it.

SOLUTION TO PROBLEMS

[014] The present inventors carried out an intensive study to reach the object described above and, as a result, found that a higher density of granular protrusions in a layer of metallic chromium improves the weldability of a sheet prepared for tinning. The present invention has thus been completed.

[015] Specifically, the present invention provides the following [1] to [6].

[016] A sheet prepared for tinning comprising, on a steel sheet surface, a layer of metallic chromium and a layer of hydrated chromium oxide stacked in this order on the side of the sheet steel, where the layer of metallic chromium has a coating weight of 65 to

200 mg / m ?, wherein the hydrated chromium oxide layer has a coating weight of 3 to 30 mg / m? in terms of the amount of chromium, and where the metallic chromium layer includes a base portion with a thickness of not less than 7.0 nm and granular protrusions provided in the base portion and with a maximum diameter of not more than 100 nm and a numerical density per unit area of not less than 200 protrusions / ym ?.

[017] The sheet prepared for tinning according to [1] above, in which the hydrated chromium oxide layer has a coating weight greater than 15 mg / m? But not exceeding 30 mg / m? in terms of the amount of chromium.

[018] The sheet prepared for tinning, according to [1] or [2] above, in which the granular protrusions have a numerical density per unit area of not less than 300 protrusions / one ?.

[019] A method of fabricating prepared tinplate to obtain the plate prepared for tinning, according to any one of [1] to [3] above, using an aqueous solution containing Cr in an amount of not less than 0, 50 mol / L and F in an amount greater than 0.10 mol / L and is free of sulfuric acid, except for sulfuric acid inevitably incorporated into it, the method comprising: the step of subjecting a steel sheet to treatment 1, including the treatment of C1 cathodic electrolysis using the aqueous solution; and the step of subjecting the steel plate to the cathodic electrolysis treatment C1 to treatment 2 including the anodic electrolysis treatment A1 and the cathodic electrolysis treatment C2 after the anodic electrolysis treatment A1, using the aqueous solution at least twice .

[020] The method of manufacturing tin-plated sheet, according to [4] above,

where an actual density of anodic electrolysis treatment A1 is not less than 0.1 A / dm ?, but less than 5.0 A / dm ?, and where an electrical quantity density of anodic electrolysis treatment A1 is not less than 0.1 C / dm ?, but less than 5.0 C / dm ?.

[021] The method of making tinplate prepared according to [4] or [5] above, in which the aqueous solution used in the treatment of cathodic electrolysis C1, the treatment of anodic electrolysis A1 and the treatment of cathodic electrolysis C2 comprises only one type of aqueous solution.

ADVANTAGE EFFECTS OF THE INVENTION

[022] The present invention provides a plate prepared for tinning with excellent weldability and a method of manufacturing it.

BRIEF DESCRIPTION OF THE DRAWING

[023] FIG. 1 is a cross-sectional view showing schematically an example of a sheet prepared for tinning of the invention.

DESCRIPTION OF THE MODALITIES Sheet prepared for tinning

[024] FIG. 1 is a cross-sectional view showing schematically an example of a sheet prepared for tinning of the invention.

[025] As shown in FIG. 1, a sheet prepared for tinning 1 includes a steel sheet 2. The sheet prepared for tinning 1 further includes, on a surface of the steel sheet 2, a layer of metal chromium 3 and a layer of hydrated chromium oxide 4 stacked on it order from the side of the steel plate 2.

[026] The metallic chromium layer 3 includes a base portion 3a covering the steel plate 2 and granular protrusions 3b provided in the base portion 3a. The base portion 3a has a thickness of at least 7.0 nm. The granular projections 3b have a maximum diameter of not more than 100 nm and a numerical density per unit area of not less than 200 projections / um ?. The metallic chromium layer 3, including the base portion 3a and the granular protrusions 3b, has a coating weight of 65 to 200 mg / m 2.

[027] The hydrated chromium oxide layer 4 is arranged on the metallic chromium layer 3 to conform the shape of the granular protrusions 3b. Does the hydrated chromium oxide layer 4 have a coating weight of 3 to 30 mg / m? in terms of the amount of chromium.

[028] The weight of the coating refers to the weight of the coating on one side of the steel sheet.

[029] The constituent elements of the invention are described in detail below.

Steel sheet

[030] The type of steel plate is not particularly limited. In general, steel sheets used as container materials (for example, a low carbon steel sheet and an ultra low carbon steel sheet) can be used. A method of making steel sheet, a material of the same and the like are also not particularly limited. The steel sheet is manufactured through a process that begins with a typical billet manufacturing process, followed by such processes as hot rolling, pickling, cold rolling, annealing and tempering rolling.

Metallic chromium layer

[031] The sheet prepared for tinning of the invention has a layer of metallic chromium on a surface of the previous steel sheet.

[032] The role of metallic chromium in the typical TFS is to reduce the exposure of a steel sheet surface that serves as the base material and thus improve the resistance to corrosion. When the amount of metallic chromium is very small, the steel sheet is inevitably exposed, and this can lead to low corrosion resistance.

[033] Is the coating weight of the metallic chromium layer not less than 65 mg / m?, Because this leads to an excellent corrosion resistance of the sheet prepared for tinning, and is preferably not less than 70 mg / m? and more preferably not less than 80 mg / m? because this leads to excellent additional corrosion resistance.

[034] On the other hand, when the amount of metallic chromium is very large, the metallic chromium with a high melting point must cover the entire surface of the steel sheet, and this induces a significant reduction in the resistance of the weld in welding and in generation significant amount of dust, which can lead to poor weldability.

[035] Does the coating weight of the metallic chromium layer not exceed 200 mg / m?, Because this leads to excellent weldability of the sheet prepared for tinning and, preferably, not more than 180 mg / m? and, more preferably, not more than 160 mg / m?, because this leads to excellent additional weldability.

Methods of measuring coating weights

[036] The weight of the coating of the metallic chromium layer and the weight of the coating of the hydrated chromium oxide layer (described later) in terms of the amount of chromium are measured as follows.

[037] First, for the sheet prepared for tinning that has formed on the layer of metallic chromium and the layer of hydrated chromium oxide, the amount of chromium (total amount of chromium) is measured with an X-ray fluorescence device. Then, the sheet prepared for tinning is subjected to alkaline treatment, that is, it is immersed in 6.5N of NaOH at 90ºC for minutes, and then again, the amount of chromium (amount of chromium after alkaline treatment) is measured with an X-ray fluorescence device. The amount of chromium after alkaline treatment is realized as the coating weight of the metallic chromium layer.

[038] Subsequently, the equation (amount of alkaline soluble chromium) = (total amount of chromium) - (amount of chromium after alkaline treatment) is calculated, and the amount of soluble alkali chromium is considered as the coating weight of the chromium oxide hydrated in terms of the amount of chromium.

[039] The metallic chromium layer as above, includes a base portion and granular protrusions provided in the base portion.

[040] Next, the portions included in the metallic chrome layer are described in detail.

Base portion of the metallic chromium layer

[041] The base portion of the metallic chromium layer serves mainly to improve corrosion resistance, covering a steel sheet surface.

[042] The base portion of the metallic chrome layer in the invention must, in addition to the corrosion resistance that is generally required of TFS, have a uniform and sufficient thickness so that the base portion is not destroyed by the granular protrusions provided in the surface layer, thus avoiding the exposure of the steel sheet, when the sheet prepared for tinning inevitably comes into contact with another sheet prepared for tinning in handling.

[043] In connection with this, the present inventors carried out a friction test of a sheet prepared for tinning with another sheet prepared for tinning in order to verify the resistance to rust and, as a result, found that when the base portion of the metallic chromium layer has a thickness of not less than 7.0 nm, the rust resistance is excellent. More specifically, the thickness of the base portion of the metallic chromium layer is not less than 7.0 nm because this leads to excellent rust resistance of the plate prepared for tinning, and is preferably not less than 9.0 nm and more preferably not less than 10.0 nm as this leads to excellent resistance to additional rust.

[044] The upper limit of the thickness of the base portion of the metallic chromium layer is not particularly limited and is, for example, not more than 20.0 nm and, preferably, not more than 15.0 nm.

Thickness measurement method

[045] The thickness of the base portion of the metallic chrome layer is measured as follows.

[046] First, a cross-sectional sample of a sheet prepared for tinning that formed a layer of metallic chromium and a layer of hydrated chromium oxide is produced by a focused ion beam method (FIB) and observed with a magnification of 20,000XK with a scanning transmission electron microscope (TEM). Then, in a sectional observation on a bright field image, focused on a portion where only a base portion is present without granular protrusions, a line analysis is conducted by energy dispersive X-ray spectrometry (EDX) to obtain intensity curves (horizontal axis: distance, vertical axis: intensity) of chromium and iron, and these curves are used to determine the thickness of the base portion. To be more specific, on the chromium intensity curve, the point where the intensity is 20% of the maximum is considered as the topmost layer, while the crossing point with the iron intensity curve is considered as the limit point with iron, and the distance between these two points is considered to be the thickness of the base portion.

[047] The coating weight of the base portion of the metallic chromium layer is preferably not less than 10 mg / m?, More preferably, not less than 380 mg / m? and even more preferably, not less than 40 mg / m?, because this leads to an excellent rust resistance of the plate prepared for tinning.

Granular protrusions of the metallic chromium layer

[048] The granular protrusions of the metallic chromium layer are formed on a surface of the base portion described above, and serve mainly to improve weldability, reducing the contact resistance between the parts to be welded of the plate prepared for tinning. The assumed mechanism of reduction in contact resistance is described below.

[049] The hydrated chromium oxide layer that covers the metallic chromium layer is a non-conductive coating and therefore has greater electrical resistance than metallic chromium, so that the hydrated chromium oxide layer works as a factor that makes welding difficult. By forming the granular protrusions on a surface of the base portion of the metallic chromium layer, the granular protrusions act to destroy the hydrated chromium oxide layer using the applied surface pressure when welded portions of the prepared tin plate come into contact with each other. with others in welding, and the granular protrusions become current welding points, so the contact resistance decreases considerably.

[050] When the number of granular protrusions in the metallic chromium layer is very small, the current points in the weld decrease in number, and this can prevent the contact resistance from being reduced, resulting in low weldability. When granular protrusions are formed to be present in high density, the contact resistance is reduced even if the hydrated chromium oxide layer, which is an insulating layer, is thick. Thus, paint adhesion, film corrosion resistance, weldability and other properties can be achieved in good balance.

[051] The numerical density of the granular protrusions per unit area is not less than 200 protrusions / um?, Because this leads to an excellent weldability of the sheet prepared for tinning, and is preferably not less than 300 protrusions / pm ?, more preferably, not less than 1,000 bumps / one? and even more preferably, more than 1,000 bumps / one? because this leads to excellent additional weldability.

[052] As a very high numerical density of granular protrusions per unit area can affect the color tone or the like, the upper limit of the numerical density per unit area is preferably no more than 10,000 protrusions / um ?, more preferably not more than 5,000 protrusions / one?, even more preferably, not more than 1,000 protrusions / one? and particularly preferably not more than 800 protrusions / um? in order to obtain an additional excellent surface appearance of the sheet prepared for tinning.

[053] The present inventors have found that when the maximum diameter of the granular protrusions of the metallic chromium layer is very large, it affects the hue or similar of the sheet prepared for tinning, and a brown pattern appears in some cases, resulting in a bad superficial appearance. The possible reasons for the above are, for example, the following: the granular protrusions absorb light of short wavelength (blue) and, consequently, the reflected light from it is attenuated, so that a reddish brown color appears; the granular protrusions diffuse the reflected light, so that the overall reflectance decreases and the color gets darker.

[054] Therefore, the maximum diameter of the granular protrusions of the metallic chromium layer is adjusted to 100 nm or less. As a result, the sheet prepared for tinning can have an excellent surface appearance. This is probably because the granular protrusions with a smaller diameter serve to suppress the absorption of light of short wavelength and to suppress the dispersion of reflected light.

[055] The maximum diameter of the granular protrusions of the metallic chromium layer is preferably not more than 80 nm, more preferably not more than 50 nm and even more preferably not more than 30 nm, because this leads to excellent surface appearance of the sheet prepared for tinning.

[056] The lower limit of the maximum diameter is not particularly limited and is preferably, for example, not less than 10 nm.

Methods of measuring the diameter of the granular protrusions and their numerical density per unit area

[057] The diameter of the granular protrusions of the metallic chromium layer and the numerical density thereof per unit area are measured as follows.

[058] First, a surface of the plate prepared for tinning having formed on it the layer of metallic chromium and the layer of hydrated chromium oxide is subjected to carbon deposition to produce an observation sample by an extraction replica method. Subsequently, a micrograph of the sample is considered at 20,000X magnification with a scanning transmission electron microscope (TEM), the micrograph taken is binarized using the software (trade name: ImageJ) and subjected to image analysis, and the diameter (as a value equivalent to the true circle) and the numerical density per unit area are determined by retroactively calculating the area occupied by the granular ridges. The maximum diameter is the diameter that is maximum in the observation fields by obtaining micrographs of five fields with a magnification of

20,000X, and the numerical density per unit area is the average of the numerical densities of the five fields.

Hydrated chromium oxide layer

[059] A hydrated chromium oxide is deposited together with metallic chromium on a surface of the steel plate and serves mainly to improve corrosion resistance. A hydrated chromium oxide also serves to improve corrosion resistance after painting, such as film corrosion resistance and paint adhesion. The coating weight of the hydrated chromium oxide layer, in terms of chromium quantity, is not less than 3 mg / m?, In order to guarantee corrosion resistance and paint adhesion of the plate prepared for tinning, and is preferably , not less than 10 mg / m? and more preferably, greater than 15 mg / m?, because this leads to excellent corrosion resistance and adhesion to additional paint.

[060] Meanwhile, a hydrated chromium oxide is inferior to the metallic chromium in conductivity and therefore an excessive amount of hydrated chromium oxide leads to an excessive resistance in welding, which can cause dust generation, splashing and a variety of weld defects, such as air bubble formation associated with over-welding, thus resulting in poor weldability of the sheet prepared for tinning.

[061] Therefore, the coating weight of the hydrated chromium oxide layer in terms of the amount of chromium is not more than 30 mg / m?, Because this leads to an excellent weldability of the plate prepared for tinning and, preferably, not more than 25 mg / m? and most preferably, not more than 20 mg / m? because this leads to excellent additional weldability.

[062] The method of measuring the coating weight of the hydrated chromium oxide layer in terms of the amount of chromium is as described above.

Method of manufacturing tin-prepared sheet

[063] Next, the method of making tin-plating sheet according to the present invention is described.

[064] The method of making tinplate prepared according to the present invention (hereinafter also referred to as the "manufacturing method of the invention") is a method of manufacturing the plate prepared for tinning of the previous invention using an aqueous solution that contains Cr in an amount not less than 0.50 mol / L and F in an amount greater than 0.10 mol / L and is free of sulfuric acid, except for the sulfuric acid inevitably incorporated in it, the method comprising: the subjecting a steel plate to treatment 1 including C1 cathodic electrolysis treatment using the aqueous solution; and the step of subjecting the steel plate to the cathodic electrolysis treatment C1 to treatment 2 including the anodic electrolysis treatment Al and the cathodic electrolysis treatment C2 after the anodic electrolysis treatment A1, using the aqueous solution at least twice .

[065] Normally, in the treatment of cathodic electrolysis in an aqueous solution containing a hexavalent chromium compound, a reduction reaction occurs on a surface of the steel plate, on which the metallic chromium is deposited, and a hydrated chromium oxide which is an intermediate product before it becomes metallic chromium is deposited on the metal chromium surface. This hydrated chromium oxide is dissolved unevenly by treating intermittent electrolysis or prolonged immersion in an aqueous solution of a hexavalent chromium compound, and in the subsequent cathodic electrolysis treatment, granular protrusions of metallic chromium are formed.

[066] As the anodic electrolysis treatment is carried out between the two cathodic electrolysis treatments, the metallic chromium is dissolved on the entire surface of the steel sheet in several places, and these places become the starting points for the formation of the granular protrusions of the metallic chromium in the treatment of subsequent cathodic electrolysis. The base portion of the metallic chromium layer is deposited in the cathodic electrolysis treatment C1 before the anodic electrolysis treatment A1, and the granular protrusions of the metallic chromium layer are deposited in the cathodic electrolysis treatment C2 after the anodic electrolysis treatment A1.

[067] The deposition amounts of these portions can be controlled by electrolysis conditions in the respective electrolysis treatments.

[068] The aqueous solution and electrolysis treatments used in the manufacturing method of the invention are described in detail below.

Aqueous solution

[069] The aqueous solution used in the manufacturing method of the invention is an aqueous solution that contains Cr in an amount of not less than 0.50 mol / L and F in an amount of more than 0.10 mol / L and is free of acid sulfuric acid, except sulfuric acid inevitably incorporated into it.

[070] The amount of F in the aqueous solution influences the dissolution of hydrated chromium oxide during immersion and the dissolution of metallic chromium during the treatment of anodic electrolysis and, therefore, greatly influences the shape of the metallic chromium deposited in the treatment of cathodic electrolysis subsequent. Sulfuric acid also has the same effect; however, the effect generated by the sulfuric acid is excessive and, as a consequence, the uneven dissolution of the hydrated chromium oxide causes the local formation of huge granular protrusions, and the dissolution of the metallic chromium proceeds extremely during the treatment of anodic electrolysis. Thus, it can be difficult to form fine granular protrusions. Therefore, the aqueous solution in the invention is free of sulfuric acid, except for the sulfuric acid inevitably incorporated in it.

[071] Sulfuric acid is inevitably incorporated into certain raw materials, such as chromium trioxide, in the industrial production process, so that the use of such raw materials results in the inevitable incorporation of sulfuric acid in the resulting aqueous solution. The amount of sulfuric acid inevitably incorporated into the aqueous solution is preferably less than 0.0010 mol / L and more preferably less than 0.0001 mol / L.

[072] The aqueous solution in the invention contains Cr in an amount of not less than 0.50 mol / L, because this leads to a highly efficient and stable deposition of metallic chromium over a long period of time.

[073] In addition, the aqueous solution in the invention contains F in an amount greater than 0.10 mol / L. As a result, the uniform and fine dissolution of the metallic chromium proceeds over the entire surface during the treatment of anodic electrolysis A1 and, consequently, generation sites in which fine granular protrusions are generated in the treatment of cathodic electrolysis C2 can be obtained.

[074] It is preferable that one type of aqueous solution is used exclusively in the treatment of cathodic electrolysis C1, in the treatment of anodic electrolysis A1 and in the treatment of cathodic electrolysis C2.

Hexavalent chromium compound

[075] The aqueous solution preferably contains a hexavalent chromium compound. The hexavalent chromium compound contained in the aqueous solution is not particularly limited, and examples thereof include chromium trioxide (CrOs), dichromates such as potassium dichromate (K2Cr207) and chromates such as potassium chromate (K2CrO4).

[076] The content of the hexavalent chromium compound in the aqueous solution is preferably from 0.50 to 5.00 mol / L and more preferably from 0.50 to 3.00 mol / L in the amount of Cr.

Fluorine-containing compound

[077] The aqueous solution preferably contains a compound containing fluorine. The fluorine-containing compound contained in the aqueous solution is not particularly limited, and examples thereof include hydrofluoric acid (HF), potassium fluoride (KF), sodium fluoride (NaF), hydrosilicofluoric acid (H2SiFs) and / or salts thereof. Examples of salts of hydrosilicofluoric acid include sodium silicofluoride (Na2SiFs), potassium silicofluoride (K2SiF6) and ammonium silicofluoride ((NHa) 2SiFs6s).

[078] The fluorine-containing compound content of the aqueous solution is preferably greater than 0.10 mol / L, but not greater than 4.00 mol / L, more preferably 0.15 to 3.00 mol / L and even more preferably, from 0.20 to 2.00 mol / L in the amount of F.

[079] The temperature of the aqueous solution in each electrolysis treatment is,

preferably, 20 ° C to 80 ° C and more preferably, 40 ° C to 60 ° C.

Treatment of C1 cathodic electrolysis (Treatment 1)

[080] C1 cathodic electrolysis treatment is carried out to deposit metallic chromium and hydrated chromium oxide.

[081] Is the electrical quantity density (the product of the current density and the current application time) in the treatment of cathodic electrolysis C1 preferably at 50 C / dm? and more preferably, 25 to 45 C / dm? in order to obtain an adequate amount of deposition and to guarantee an appropriate thickness of the base portion of the metallic chromium layer.

[082] The current density (unit: A / dm?) And the current application time (unit: second) are adjusted accordingly based on the previous electrical quantity density.

[083] C1 cathodic electrolysis treatment need not be continuous electrolysis treatment. In other words, the C1 cathodic electrolysis treatment can be an intermittent electrolysis treatment because electrolysis is performed separately for each set of electrodes in industrial production and, consequently, a period of immersion without current application is inevitably present. In the case of intermittent electrolysis treatment, the density of the total electrical quantity preferably falls within the previous limits.

A1 anodic electrolysis treatment

[084] The anodic electrolysis treatment A1 serves to dissolve the metallic chromium deposited in the treatment of cathodic electrolysis C1, in order to form the generation sites of the granular protrusions of the metallic chromium layer to be generated in the treatment of cathodic electrolysis C2.

[085] When dissolution occurs excessively in the treatment of anodic electrolysis A1, this can cause a reduced number of generation sites and, therefore, a lower numerical density of granular protrusions per unit area,

variation in the distribution of granular protrusions due to the uneven progress of dissolution and a small thickness of the base portion of the metallic chromium layer below 7.0 nm.

[086] In addition, when the current density of A1 anodic electrolysis treatment is very high, this can adversely affect corrosion resistance and other properties. This is probably because part of the metallic chrome layer is dissolved more than necessary and, consequently, the generation sites with the base portion of the metallic chrome layer with a thickness of less than 7.0 nm are formed locally.

[087] The metallic chromium layer formed through the cathodic electrolysis treatment C1 and the first anodic electrolysis treatment A1 is mainly the base portion. To have the base portion of the metallic chromium layer with a thickness of 7.0 nm or more, is it necessary to guarantee the amount of metallic chromium not less than 50 mg / m? after the treatment of cathodic electrolysis C1 and the first treatment of anodic electrolysis A1.

[088] Thus, in order to facilitate the formation of the metallic chromium layer with the granular protrusions in the subsequent cathodic electrolysis treatment C2, the current density of the anodic electrolysis treatment A1 (that is, the current density of each of the anodic electrolysis A1 which are carried out at least twice) is properly adjusted, and is preferably not less than 0.1 A / dm ?, but less than 5.0 A / dm ?.

[089] A current density of not less than 0.1 A / dm? it is favorable because this leads to the formation of a sufficient number of generation sites of the granular protrusions, which facilitates the generation and uniformly sufficient distribution of the granular protrusions in the treatment of subsequent cathodic electrolysis C2.

[090] A current density less than 5.0 A / dm? it is favorable because it leads to excellent rust resistance and corrosion resistance of the film. This is probably because the metallic chromium is prevented from dissolving in an unnecessarily excessive amount in a single anodic electrolysis treatment, so that the sites of generation of the granular protrusions do not grow excessively, thus preventing the base portion of the metallic chromium layer. become locally thin.

[091] The electrical quantity density of the A1 anodic electrolysis treatment (that is, the electrical quantity density of each of the A1 anodic electrolysis treatments that are carried out at least twice) is preferably not less than 0, 1 C / dm ?, but less than 5.0 C / dm ?. The lower limit of the density of the electrical quantity in the treatment of anodic electrolysis is preferably greater than 0.3 C / dm ?. Is the upper limit of the density of the electrical quantity in the treatment of anodic electrolysis preferably not greater than 3.0 C / dm? and more preferably not more than 2.0 C / dm ?. The density of the electrical quantity is a product of the current density and the current application time.

[092] The current application time (unit: second) is adjusted accordingly based on the previous current density (unit: A / dm?) And the electrical quantity density (unit: C / dm?).

[093] A1 anodic electrolysis treatment need not be a continuous electrolysis treatment. In other words, the anodic electrolysis treatment A1 can be an intermittent electrolysis treatment because electrolysis is carried out separately for each set of electrodes in industrial production and, consequently, a period of immersion without current application is inevitably present. In the case of intermittent electrolysis treatment, the density of the total electrical quantity preferably falls within the previous limits.

Treatment of C2 cathodic electrolysis

[094] As described above, cathodic electrolysis treatment is carried out to deposit metallic chromium and hydrated chromium oxide. In particular, the C2 cathodic electrolysis treatment allows granular protrusions of the metallic chromium layer to be generated at previous generation sites, serving as starting points. In this process, when the density of the electrical quantity is very high, the granular protrusions of the metallic chromium layer can grow excessively, leading to a coarse grain size.

[095] For this reason, the density of the electrical amount of the C2 cathodic electrolysis treatment (i.e., the density of the electrical amount of each of the C2 cathodic electrolysis treatments that are performed at least twice) is preferably lower at 30.0 C / dm ?, more preferably not more than 25.0 C / dm? and, even more preferably, not more than 7.0 C / dm ?. Is the lower limit not particularly limited and is it preferably not less than 1.0 C / dm? and most preferably, not less than 2.0 C / dm ?.

[096] The current density (unit: A / dm?) And the current application time (unit: second) are adjusted accordingly based on the previous electrical quantity density.

[097] C2 cathodic electrolysis treatment need not be a continuous electrolysis treatment. In other words, the C2 cathodic electrolysis treatment can be an intermittent electrolysis treatment because electrolysis is carried out separately for each set of electrodes in industrial production and, consequently, a period of immersion without current application is inevitably present. In the case of intermittent electrolysis treatment, the density of the total electrical quantity preferably falls within the previous limits.

Number of treatment times 2 including A1 and C2

[098] In the manufacturing method of the invention, the steel sheet subjected to the cathodic electrolysis treatment C1 is subjected to treatment 2 including the anodic electrolysis treatment A1 and the cathodic electrolysis treatment C2 at least twice.

[099] The number of times of treatment 2 is preferably at least three, more preferably at least five and even more preferably at least seven. When treatment 2, as above, is repeated, it means that the formation of the granular protrusion generation sites of the metallic chromium layer (anodic electrolysis treatment A1) and the formation of the granular protrusions of the metallic chromium layer (electrolysis treatment) cathodic C2) are repeated; therefore, the granular protrusions of the metallic chrome layer can be uniformly formed at high density. Because of this configuration, even when the coating weight of the hydrated chromium oxide layer is increased to improve corrosion resistance and other properties, the granular protrusions that are uniformly present at high density act to increase the number of contact points in the welding, thus reducing contact resistance and achieving excellent weldability.

[0100] The upper limit on the number of times of treatment 2 as above is not particularly limited; however, in order to control the thickness of the base portion of the metallic chromium layer formed in the treatment of cathodic electrolysis C1 to a suitable range, treatment 2 is preferably not repeated excessively and is, for example, repeated up to 30 times and preferably up to 20 times.

After treatment

[0101] Treatment 2, including Al anodic electrolysis treatment and C2 cathodic electrolysis treatment, can be followed by post-treatment.

[0102] For example, to ensure paint adhesion and film corrosion resistance, the steel sheet can be subjected to immersion treatment or cathodic electrolysis treatment using an aqueous solution containing a hexavalent chromium compound for control purposes of the amount of hydrated chromium oxide layer, modify that layer and other purposes.

[0103] Even when the above post-treatment is carried out, the thickness of the base portion of the metallic chromium layer and the diameter and numerical density of the granular protrusions are not affected by this.

[0104] The hexavalent chromium compound contained in the aqueous solution used in the post-treatment is not particularly limited, and examples of it include chromium trioxide (CrO3), dichromates, such as potassium dichromate (K2Cr207) and chromates, such as chromate potassium (K2CrO + 4).

EXAMPLES

[0105] The present invention is specifically described below with reference to examples. However, the present invention should not be construed as being limited to the following examples.

Manufacture of sheet prepared for tinning

[0106] Each steel plate (tempered class: TACA) as produced with a steel plate thickness of 0.22 mm was subjected to normal degreasing and pickling. Subsequently, the relevant aqueous solution shown in Table 1 below was circulated by a pump at a rate equivalent to 100 mpm in a fluid cell, and the electrolysis treatment was carried out using lead electrodes under the conditions shown in Table 2 below, thus manufacturing a plate prepared for tinning which is TFS. The plate prepared for tinning, as manufactured, was washed with water and dried by a blower at room temperature.

[0107] To be more specific, first, treatment 1 including cathodic electrolysis treatment C1, and treatment 2 including anodic electrolysis treatment A1 and cathodic electrolysis treatment C2, were performed in this order using one of the aqueous solutions A a D. The number of times for treatment 2 was two or more, while treatment 2 was performed only once in some comparative examples. In some examples, treatment 2 was followed by

treatment (cathodic electrolysis treatment) using an aqueous solution E.

[0108] Regarding the cases in which the treatment, including the anodic electrolysis treatment A1 and the cathodic electrolysis treatment C2, was carried out two or more times, the current density and the electrical quantity density shown in Table 2 below were the values at a time.

[0109] For example, in Example 1 (number of times 2: 2 treatment) shown in Table 2 below, was the first C2 cathodic electrolysis treatment performed with a current density of 60.0 A / dm? and an electrical quantity density of 9.0 C / dm ?, and the second treatment of cathodic electrolysis C2 was carried out with a current density of 60.0 A / dm? and an electrical quantity density of 9.0 C / dm ?.

Coating weight

[0110] For each of the sheets prepared for tinning manufactured, the weight of the coating of the metallic chromium layer (metal layer Cr) and the weight of the coating of the hydrated chromium oxide layer (layer of hydrated Cr oxide) in terms amount of chromium (indicated simply as “coating weight” in Table 3 below) were measured. The measurement methods are as described above. The results are shown in Table 3 below.

Cr metal layer structure

[0111] For the metal layer Cr of each of the plates prepared for tinning, the thickness of the base portion and the maximum diameter and the numerical density per unit area of the granular protrusions were measured. The measurement methods are as described above. The results are shown in Table 3 below.

Evaluation

[0112] The sheets prepared for tinning manufactured were evaluated by the following factors. The results of the assessment are shown in Table 3 below.

Rust resistance 1: Rust resistance test of worn steel plate

[0113] A rust resistance test of a worn steel plate is performed to assess rust resistance. Specifically, two samples were cut from each of the plates prepared for tinning. One sample (30 mm x 60 mm) was attached to a friction tester to be used as an evaluation sample, while the other sample (10 mm x 10 mm) was attached to a head, and the head was moved with 10 movements over a length of 60 mm at a surface pressure of 1 kgf / cm? and at a friction rate of 1 second by reciprocity. Subsequently, the evaluation sample was allowed to rest in a chamber of constant temperature and humidity at 40ºC and 80% relative humidity for 7 days. Then, the evaluation sample was observed at low magnification with an optical microscope, and a micrograph of it was subjected to image analysis to determine the fraction of the rust area of a rubbed portion. The evaluation was carried out according to the following criteria. For practical use, when the result is A, B or C, the sheet prepared for tinning can be classified as having excellent resistance to rust.

A: A fraction of the rust area less than 1% B: A fraction of the rust area not less than 1% but less than 2% C: A fraction of the rust area not less than 2% but less than 5% D: A fraction of the rust area of not less than 5% but less than 10% E: A fraction of the rust area of not less than 10%, or rust elsewhere than a rubbed part.

Rust resistance 2: Storage rust test

[0114] 20 samples of 100 mm x 100 mm were cut from each sheet prepared for tinning manufactured, stacked, wrapped with anti-rust paper, sandwiched by pieces of plywood to be fixed in this way, and then left to stand in a chamber constant temperature and humidity at 30ºC and 85% relative humidity for 2 months. Subsequently, the fraction of the rust area that occurred on overlapping surfaces (fraction of the rust area) was observed and evaluated according to the following criteria. For practical use, when the result is A, B or C, the sheet prepared for tinning can be classified as having excellent resistance to rust.

A: No rust B: A very small rust or a fraction of rust area less than 0.1% C: A fraction of the rust area not less than 0.1% but less than 0.3% D: A fraction of the rust rust area not less than 0.3% but less than 0.5% E: A fraction of the rust area not less than 0.5% Surface appearance (color tone)

[0115] For each of the plates prepared for tinning manufactured, the value of L was measured according to the measurement of the color difference of the Hunter type defined in JIS Z 8730 of the old version (1980) and evaluated according to the following criteria . For practical use, when the result is A, B or C, the sheet prepared for tinning can be classified as having an excellent surface appearance.

A: an L value of not less than 69 B: an L value of not less than 67, but less than 69 C: an L value of not less than 65 but less than 67 D: an L value of not less than 63, but less than 65 E: An L value less than 63 Weldability (contact resistance)

[0116] Each of the plates prepared for tinning manufactured was subjected to heat treatment of 210ºC x 10 minutes twice, and then the contact resistance was measured. More specifically, the samples from each plate prepared for tinning were heated (and held at a target plate temperature of 210ºC for 10 minutes) in a batch oven, and the samples subjected to heat treatment were superimposed. Subsequently, 1% mass of DR type Cr-Cu electrodes was machined to a tip diameter of 6 mm and a curvature of R40 mm, the overlapping samples were sandwiched by these electrodes and retained at a pressure of 1 kgf / cm ? for 15 seconds, then a current of 10A was supplied to it, and the contact resistance between the sample plates was measured. The measurement was performed in ten cases, and the average was considered as a contact resistance value to be evaluated according to the following criteria. For practical use, when the result is AA, A, B or C, the sheet prepared for tinning can be classified as having excellent weldability.

AA: Contact resistance not exceeding 20 uOQ A: Contact resistance greater than 20 uO, but not exceeding 100 nO B: Contact resistance greater than 100 uO, but not exceeding 300 nO C: Contact resistance greater than 300 nuOQ, but not more than 500 pOQ D: Contact resistance greater than 500 uO but not greater than 1000 uO E: Contact resistance greater than 1000 uO Adhesion to primary paint

[0117] Each of the plates prepared for tinning manufactured was applied with epoxy-phenolic resin and subjected to heat treatment of 210ºC x 10 minutes twice. Subsequently, the cuts reaching the steel plate were made at 1 mm intervals in a grid pattern. The peeling was performed with adhesive tape, and the peeling status was observed. The fraction of the peeled area was evaluated according to the following criteria. For practical use, when the result is A, B or C, the sheet prepared for tinning can be classified as having excellent adhesion to the primary paint.

A: A fraction of the peeled area of 0% B: A fraction of the peeled area greater than 0%, but not exceeding 2% C: A fraction of the peeled area greater than 2%, but not exceeding 5% D: A fraction peeled area greater than 5%, but not exceeding 30% E: A fraction of the peeled area greater than 30% Adhesion to secondary paint

[0118] Each of the plates prepared for tinning manufactured was applied with epoxy-phenolic resin and subjected to heat treatment of 210ºC x 10 minutes twice. Subsequently, cuts reaching the steel plate were made at 1 mm intervals in a grid pattern, the retort treatment was carried out at 125ºC for 30 minutes. After drying, peeling was performed with adhesive tape, and the peeling state was observed. The fraction of the peeled area was evaluated according to the following criteria. For practical use, when the result is A, B or C, the sheet prepared for tinning can be classified as having excellent adhesion to the secondary paint.

A: A fraction of the peeled area of 0% B: A fraction of the peeled area greater than 0%, but not exceeding 2% C: A fraction of the peeled area greater than 2%, but not exceeding 5% D: A fraction peeled area greater than 5% but not greater than 30% E: A fraction of the peeled area greater than 30% Resistance to corrosion of the film

[0119] Each of the plates prepared for tinning manufactured was applied with epoxy-phenolic resin and subjected to heat treatment of 210ºC x 10 minutes twice. A cross cut was made reaching the steel plate, and the plate prepared for tinning was immersed in a test solution that was a mixed aqueous solution of 1.5% citric acid and 1.5% NaCl at 45ºC for 72 hours. . Immersion was followed by rinsing and drying, and then strip stripping was performed.

The peeled width (that is, the total width of the peeled portions that extends to the right and left from a cut portion) was measured at four locations within 10 mm of the crossing point of the cross cut, and the mean of the measurements at the four sites it was obtained.

The average peeled widths were defined as a corroded width per film and evaluated according to the following criteria.

For practical use, when the result is A, B or C, the sheet prepared for tinning can be classified as having excellent corrosion resistance under the film.

A: corroded width not exceeding 0.2 mm B: corroded width greater than 0.2 mm, but not exceeding 0.3 mm C: corroded width greater than 0.3 mm, but not exceeding 0, 4 mm D: Corroded width greater than 0.4 mm, but not greater than 0.5 mm E: Corroded width greater than 0.5 mm Table 1 Solution 5 a - | 0rOs 0.50mol / L NaF 0.20mol / L Cro; 0.75 mol / L NaF 0.20 mol / L c CrO; 1.00mol / L NaF 0.20mol / L CrO; 0.50 mol / L NaF 0.10 mol / L E Cro; 0.60mol / L NH, F 0.048mol / L

Table 2 Table 2 (1/2)

Table 2 (1/2) Treatment 1 and Treatment 2. Temeno Tome [Er FE ===

Number of | Only! Fears Gumens | meets | cumene] Heal | Eeete [urens] Curans [mec [Emas | 4 [cumene paddle [Guys] Eeceio Ten | apalication | quantity | Cure: | application | quantisy | STS tº [application | quantty |, Los o and TaL | application | auanti SNS | time | density [9999 | time | density [OM] time | density [Montmont2 NS time | density [e [aan] seo cam ban | seo [pray [aan] seo [oa | Led to Das | 600 | o8 | 390 | 10 | o50 | os | 600] om | just a [ez | to Pas | 600 | 0685 | 390 | 20 Pos A oo as aC es | to Pas | 600 | o6 | 390 | so | os50 [2 oo os aC [es | the Pas 600 | o68 | 390 | 20 | 050 [| 1 1 600] om [6 to Pp [es | the fans [600 | 0865 | 390 f 20 | os0 [4 | oo | oo aa [es | the fans [600 | 085 | 290 f 20 | os0 [1 | 600 | cos Tao [er | the fans [600 | 085 | 390 [20 | os0 [4 600 | cos to Les | the fans [600 | 08 | 390 | 20 [os [1 6oo | ow | just pe o oso | o | Les | to Tas | 600 | o8 | 390 | 20 os [17 600] om [6 2 pe o os | oso [125 | [and] the Pas 600 | os | 390 | 19 | o50 | os | 600] oo5 [30 to Pe fo | 25 | os0 [125] [me | f 600 fans | 065 | 390 20 | 050 [1 | 600] om so Pa and o as [oo [150 | [ext | the fans [600 | 06 | 390 20 | o50 [| 1 | 600] om [only to E to as [150 [225 | [exi | f 600 fans | 086 | 390 20 | os0 [| 1 | 600 | oos [ao ae o as [oso [75 | [me | the fans [600 | 085 | 290 [20 | os0 [7 | 600] om eo Da as [oo [150 | Les da Pas 600 | 0685 | 390 | 29 [os [7 6oo | oo [ps air and os | oo [150 | Lexcs to Pas 600 | 085 | 390 | 29 [os [7 600 | oos5 [to De a as oo [159 | Leds Das | 600 | 050 | 300 | 19 | os0 | os] sounds to [es and Pas 600 | o50 | 300 | 29 | o50 [7 1 600] om so a [exis | and fans [600 | 030 [180 Po | os0 [2 | oo | ao o a [ex | and fans [600 | 050 | 300 20 | os0 [4 | 600 | oo o Lex | and Das | 600 | os50 | 300 | 29 | it sounds | oo | a [ex | and Das | 600 | o50 | 300 | 29 Pos oo to Lex | and Das | 600 | o50 | 300 | 29 os [7 600] om [6 Dae o as | bone [175 | Lex | and [as | 600 | o50 | 300 | 209 | o50 [7 600] om [6 da de as oo [150) EX: Example Table 2 (2/2)

Teble 2 (2/2) Treatment 1 and Treatment 2. = Nisa + LeE = E == EF == a Temo. ument | Eletric urent | Electro ument | Electro | Numbenof | ument salt | Electio cen agro aus fame Sm [025 fores aa aus [une | 8 free or om [00 Sensi time | density | CS | time | Optimal density | density and time | density [o [aan] seo | cam aan] so [pray [Want] seo | pray | [ease fas | 600 | 050 | 300 | 20 | o50 | 1 | 600 (om [ar [5 Pe fo 15 [100 [159] [ex | 6 fans [600 | 050 | 300 | 20 | o50 | 1 | 600] oo (to Dre o as [100 [150 | [ex | o fas [600 | os50 | 300 Pio | oso | os | sounds to oa [ex | o fas [600 | os50 | 300 P 20 | os0 [| oo | oo oa Lex | ec Das | 600 | os50 | 300 | so | os0 | 2) 6oo | om | so Lexso | ec Pas | 600 | o50 | 300 | 209 os [7] 600 | ot | 6o to Les] and Pas 600 | o50 | 300 | 29 | o50 [| 7 1 600 ] oo [ar PR [Lex | e fas | 600 | os0 | 300 | 20 | os A oo to a O [ess | ec Pas 600 | 050 | 300 | 20 | o50 [| 7 | 6] om [6 | 2 fe fo 15 | os [75 | [ex | o fas f 600 | 050 | 300 20 | o50 [1 | 600 | om 6 a PE o as [oo [159 | [ex | o fas [600 | o50 | 300 [ 20 | os0 [1 | 600 | with air Ds and o as [oo [150 | Lexas | o Pas | 600 | os0 | 300 | 29 | os6 1) 600 | oos | to Pe o as oo [150 | [es] Das | 600] 06 | 390 | os | oso0 | 025 | 600] o the Lexas PRP | the fans | 600 | o65 | 390 ps as a aa aa Lex a Tas | 600 | os | 390 | in the pose o a o a a O O [exso | to Tas | 600] o6s | 390 | 30 | os0 | 15 | 600] o o Pa Less da Pas 600 | 0686 | 390 | 45 | o50 | 225] 600 | om | ag a [ese | the Das 600 | 08 | 390 | 45 | 050 | 225 | 600] om | 6th to [est | pp Tas | 600 | o50 | 300 | 209 | os50 [7 600 | 025 [to the o [| es2z | to Pas | 600 | 07% | 420 | 20 | 050 [| 1 | 600] ow [oo Da Pe o as | bone [175 | [ess | a [as | 600 | 020 [120 | 20 [| os50 | 1 600] dog so Pp

EX: Example CE: Comparative example

Table 3 Table 3 (1/2) Table 3 (1/2) Porcelain coating granular lenses Re Diam gem 2 | sound the | ssa | E = Thick. the gom fp de in the paint under ii the sec. pelíci- 2 for Jones 6 | to | to Poa poa [PA AB [o [Lex2z [rs | a | 1st jo7o | o ja [e je [oa A e [| pes fins a Jor | go PD o pa PB and PA A BB [o [Lex fons 5 | 1oo joao | to | a [e ja DA AB [[Lexs fo | 5 1 165 | to [pa pa A e ço [exe [1 | 5 1 108 | 30 [| oo JJ a fe | a fa ja De [ço ez iso 5 Pons 2 DD 130 | a [Pe | a [a [a | and [cc) [exe [140 | nn | 1st js | 26 jo a [Pe | ec [a ja A [| and [ex fis | 18 os so Dão [pa PB dB DA A A [A [Lexio [118 | 19 | the joso | to | a [Poa from DA A A [A Lex [15 | 22] 108 | so [to pa dB A A A A [Lexiz [15 | 28 1] 108 | so [| 3 Jo a pe dB A A A A [exis [no 17 Pros Pas ao AA A [A [exis [15 | 2] 100 | to [so Ja pe dA A A A A [Les Pirro | 18 Jos Pao PD so pa DB A PA A A [A [thin exis | 19 | os | to | bone | the [| and | the [| a | a | a | a | [Lexiz [iso (at 125 | o [to AA and ço [Lee fis 6 Pons poxo Pp o | a [PB dB DA A Be [[there are wires | a Jo7g jog | oo | and Poe dB DA Ag [| [Lexzo [110 | 5 1 105 | ao [so po PB AAA and Lex yarns | 5 Jo dao o Ag O [exza [12 | 5 1 12% | 3 [mo Ja fe | a Da A De [ço [Lex [1237 17 Dona Jo [the pa PB AAAA [Lea [110 | 2 Jos Dao Paso [| a [DB A [AA DA [A | EX: Example

Table 3 (2/2) So coating | ee Resist | Res | Avaré | sum | ace | go is fo atemo | sine ca oibda- sãoà | healthy are sea to om | so polco- [mem] memo nm nm Pprotusions / une | d Lexas Pro to A A [ex [120 | 2 | 120 30 PD ro Pa A AA [A [A Da A ra aa oa tion o Lexas Pra a o g ation [Lex 1a Ds ao BA aee [exso [130 6 Ps Po s AA DB ear ra oa o o [Lex ras a to the RA Lexa ra to the og RC [exsa [130 [2 Ps Po May AA DA a [exs Jin [5 108 [506 P 36 |] a Pp AAAA | Be | c | [Lexss 16 | 5 | 105 | 6 | 30 | Pp AB | A | A | B | c | Lexso Pre to O o AB [ex F1s [to Jor [Ds Poco | a PB A A | B | c | [Lex fo a o o o CA A DB and ear as a o o O ÇÕ e e ro a E A ÇÕO ee Proo a [this To Ds are O o A a [e EX: Example EC: Comparative example

[0120] As is evident from the results shown in Table 3, it was revealed that the sheets prepared for tinning of Examples 1 to 42 were excellent in weldability and also in rust resistance, under resistance to film corrosion and paint adhesions ( primary and secondary). On the other hand, the plates prepared for tinning of Comparative Examples 1 to 3 exhibited insufficient weldability, and some comparative examples were insufficient in resistance to rust and / or adhesion to the paint.

LIST OF REFERENCE SIGNS 1: sheet prepared for tinning 2: steel sheet 3: metallic chromium layer 3a: base portion 3b: granular protrusion 4: hydrated chromium oxide layer

Claims (6)

1. Sheet prepared for tinning, CHARACTERIZED by the fact that it comprises, on a steel plate surface, a layer of metallic chromium and a layer of hydrated chromium oxide stacked in this order on the side of the steel sheet, where the layer metal chromium has a coating weight of 65 to 200 mg / m ?, whereas the hydrated chromium oxide layer has a coating weight of 3 to 30 mg / m? in terms of the amount of chromium, and where the metallic chromium layer includes a base portion with a thickness of not less than 7.0 nm and granular protrusions provided in the base portion and with a maximum diameter of not more than 100 nm and a numerical density per unit area of not less than 200 protrusions / pm ?. 2. Sheet prepared for tinning according to claim 1, CHARACTERIZED by the fact that the hydrated chromium oxide layer has a coating weight of more than 15 mg / m? But not more than 30 mg / m? in terms of the amount of chromium. 3. Plate prepared for tinning according to claim 1 or 2, CHARACTERIZED by the fact that the granular protrusions have a numerical density per unit area of not less than 300 protrusions / yum ?. 4. Method for the manufacture of sheet prepared for tinning to obtain the sheet prepared for tinning, according to any one of claims 1 to 3, CHARACTERIZED by the fact that it uses an aqueous solution containing Cr in an amount of not less than 0.50 mol / L and F in an amount greater than 0.10 mol / L and is free of sulfuric acid, except for sulfuric acid inevitably incorporated into it, the method comprising: the step of subjecting a steel sheet to treatment 1, including treatment of C1 cathodic electrolysis using the aqueous solution; and the step of subjecting the steel plate to the cathodic electrolysis treatment C1 for treatment 2, including the anodic electrolysis treatment A1 and the cathodic electrolysis treatment C2 after the anodic electrolysis treatment A1, using at least two aqueous solutions times. 5. Method of fabrication of sheet prepared for tinning, according to claim 4, CHARACTERIZED by the fact that the current density of the A1 anodic electrolysis treatment is not less than 0.1 A / dm?, But less than 5.0 Aldm ?, and where an electrical quantity density of the anodic electrolysis treatment A1 is not less than 0.1 C / dm ?, but less than 5.0 C / dm ?. 6. Method of manufacturing tin-plated sheet according to claim 4 or 5, CHARACTERIZED by the fact that the aqueous solution used in the treatment of cathodic electrolysis C1, the treatment of anodic electrolysis A1 and the treatment of cathodic electrolysis C2 comprises just one type of aqueous solution.